Note: Descriptions are shown in the official language in which they were submitted.
3~7 ~
BACKGROUND OF THE INVENTION
This invention relates -to a process for converting coal
to low-sulfur and low-ash gaseous, liquid and solid fuels, and
more particularly, to a process for supplying the energy require-
ments of a steel plant from an ash- and sulfur-containing coal.
The primary source of energy for the steel industry
continues to be coke for the blast furnace. The conventional
method for coke manuf~cture, that is, by slot ovens, requires
a blend of high and low volatile coals of proper swelling
properties to produce a strong coke without damaging t~le ovens.
Beyond these physical properties, there is a need for desirable
chemical properties (i.e. low ash and sulfur content) to permit
low-cost production of high quality hot metal. With the continued
expansion of the worldls productive capacity for steel, a grow~
ing shortage of good metallurgical coals is developing, particu-
larly those having the essential low volatile coal ingredients.
Low-sulfur coals also are ln short supply because the electric
utilities now compete for such coals to satisfy environmetal
requirements
In addition to the energy supplied by coke and coke
oven by-products, the steel industry consumes liquid and gaseous
fuels for blast furnace injection, soaking pits, reheat furnaces,
steam and power generation, etc. Future supplies oE these fuels
are also in jeopardy.
There are extensive reserves of coals in the United
States, and in other parts of the world as well, suf~icient in
fact, to satisfy a substantial part of the energy needs of the
world for centuries to come. Unfortunately, these coals in -their
indigenous state are not suitable for use either as clean fuel,
i.e. low ash- and low sulfur-containing, or as feedstock for coke
; manufacture.
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7~
Accordingly, the primary object of the present
invention is to provide a process for converting any coal, by
itself, whether it be caking or non-caking, low sulfur or high
sulfur, low ash or high ash, low volatile or high volatile, to
a desired spectrum of clean gaseous, liquid and solid fuels.
The solid fuel, for purposes of a steel plant, is coke, or
formcoke. The term "formcoke" defines coke o~tained by the
calcination of preformed or preshaped carbonaceous solids and
is used to distinguish from coke obtained as broken pieces of
all sizes and shapes from conventional coke ovens.
The prior art is represented by the following patents
and publications:
U.S. 1,925,505 - Rose - Aug. 29, 1933
2,166,321 - Pott - July18, 1939
2,664,390 - Revere et al. - Dec.29, 1953
2,686,152 - Franke - Aug~10, 1954
3,018,242 - Gorin - Jan.23, 1962
3,240,566 - Bullough et al. - Mar.15, 1966
3,401,089 - Friedrich et al. - Sept. 10, 1968
203,562,783 - Gorin - Feb.9, 1971
3,748,254 - Gorin - July24, 1973
3,791,956 - Gorin et al. - Feb.12, 1974
German Pat. No. 320,056 - Rutgerswerke AG- Apr. 21, 1920
"Process for the Solvent Extraction of Coal"
Bureau of Mines Informatlon Circular - I.C. 7420 (Oct. 1947)
"Pott-Broche Coal-Extraction Process and Plant
of Ruhrol G.m.b.~l., bottrop-Welheim, Germally".
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~S;~7 ~ ~
SUr~MARY OF THE INVENTION
The present invention is an improvement ln the
process for liquefaction of coal by solvent extraction which
comprises, in its broadest aspects, the following essential
operations:
.~ (1) Simultaneous solvent extraction and hydrotreatment
of the coal in a coal liquefaction zone under
hydrodesulfurizing conditions selected -to yield
a coal extract having a lower organic sulfur
content than the coal;
(2) separation of the liquefaction product into at
least two parts, the first part being a low
solids-containing product containing said coal
extract, and the second part being a high
solids~containing product containing said
undissolved ash-containing hydrocarbonaceous
residue;
(3) treatment of the first part, as follows:
(a) recovery of the major portion of the
; 20 solvent for recycle to the liquefaction zone;
- (b) production of a pelletizable mixture
of coal extract and carbonaceous solids;
(c) formation of pellets from the
pelletizable mixture; and
(d) induration of the pellets, concurrent
with, or subsequent to their formation,
to form hardened low-ash and low-sulfur
pellets;
(4) treatment of the second part, as follows:
(a) distillation of the second part to
yield a hydrocarbonaceous ash-
containing solid and a hydrocarbonaceous
distillate; and
(b) reaction of said hydrocarbonaceous ash- -
containing solid with steam in a steam-
carbon gasification zone to yield a gaseous
product and ash-containing inc,rgani~ sulfur;
(5) recovery of a hydrocarbonaceous distillate fraction
from said hydrocarbonaceous distillate for use
as solvent in the liquefaction zone; and
(6) treatment of the gaseous product from the gasifi-
cation zone to yield a methane-rich gas and
hydrogen for use in the liquefaction zone.
"
The advantages of th~ process of the present
invention include the following:
` (1) A single coal, whether it be caking or non-caking,
high sulfur or low sulfur, high volatile or low
; 20 volatile, high ash or low ash, may be used to
satisfy the energy requirements of an ore reduction
plant.
(2) The process may be readily operated continuously
to yield a spectrum of fuels whose distibution
and respective compositions may be regulated in
response to conditions maintained in the coal
liquefaction zone and the separation zone.
(3) The process permits autogenous maintenance of
solvent balance and hydrogen requirements.
`';
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,'.~' ' ,
(4) The process is especially valuable in its appli-
cation to high-sulfur and high-ash coals. A
variety of asn-free fuels which are substantially
free of inorganic sulfur a~,d much reduced in
organic sulfur may be readily obtained as will
,~r be apparent from the following more detailed
; description of the invention in its broadest
aspect and in its preferred embodiment.
!.~
- DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a schematic flowsheet of the present
invention in its broadest aspects; and
FIGURE 2 is a schematic flowsheet of the pr~ferred
embodiment of the present invention.
THE INVENTION
(in its broadest aspects)
Liquefaction
Referring to FIGURE 1, coal and liquefaction solvent
are intrcduced into a coal liquefaction zone 10. The coal is
introduced through line 11. The liquefaction solvent is
introduced through lines 12 and 13.
Any coal may be used in the process of this inven-
tion, non-limiting examples of which are lignite, bituminous
coal and sub~bituminous coal. The coal may be non-caking,
weakly caking or caking. It may be low in sulfur or high
j in sulfur, or in between; it may be low in ash or high in
ash, or in-between; or it may be low volatile or high volatile,
or in-between. The process of the present invention is of
- especial value in the case of non-caking or weakly caking
coals and high-sulfur coals since normally such coals have
only lim,ted utility.
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'
A sui.table liquefaction solvent is a mixture o:F
polycyclic, aromatic hydrocarbons which is liquid under the
conditions of temperature and pressure maintained during coal
liquefaction. A suitable boiling range for such a solvent,
for example, is within the range 230 to 475C. The solvent
may be conveniently derived as a distillate fraction from one
or more of the unit operations of the present process.
The selected coal, in a finely divided state, is
subjected to simultaneous solvent extraction and hydro-
treatment in the liquefacti.on zone 10 under hydrcdesulfurizingconditions. The extraction operation may be any of those used
by those skilled in the art, fcr example, continuous, batch,
countercurrent or staged extraction. Hydrogen for the hydro-
- treatment may be supplied as gaseous hydrogen, or by means of
a hydrogen-donor solvent. If gaseous hydrogen is used, the
solvent may be any suitable polycyclic aromatic hydrocarbon, or
: mixtures of polycyclic aromatic hydrocarbons which are liquid at
. the temperature and pressure of extraction. If a hydrogen-donor
solvent is required, at least a portion of the polycyclic
aromatic hydrocarbons is partially hydrogenated. Such a solvent
is rehydrogenated to maintain its effectiveness as a hydrogen
donor.
The conditions maintained in the extraction zone
are those which are effective in desulfurizing the extract, that
is, in reducing the organic sulfur content of the extract. Those
conditions are generally known and are typically as follows:
t; Gaseous Hydrogen H-Donor
: Temperature,C. 400-450 400-450
Pressure, Kg/cm2 70-200 5- 50
H addition, Wt.~ MAF* coal0.70-2.5 0.70-2.5
Solvent to Coal (wt. ratio)1.5-3.0 1.5-3.0
*MAF is moisture- and ash-Eree coal
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;
r~
The product consists of an effluent: gas (eontainincj H2S) whieh
is rejeeted through a line 14 and an effluent slurry product
(containing solvent, extract and undissolved hydrocarbonaceous
solids and ash) whieh is conducted by a line 15 to a separation
zone 16.
Separation of the Extraction Slurry
_ . .
Separation of the effluent slurry from the liquefae-
tion zone into at least two parts is effeeted in the separation
zone 16 at elevated temperature, generally elose to that of the
liquefaction zone. The first part is a low solids-containing
produet eontaining eoal extraet and solvent. The second part is
a high solids-containing slurry product eontaining eoal extraet,
solvent and the major portjon of the undissolved ash-containing
hydrocarbonaeeous solids. The separation may be aeeomplished
by settling, hydroelones, eentrifugation, filtration or by a
eombination of two or more of these unit operations.
Cooling of the extraetion slurry before separation
may result in seleetive preeipitation of some of the higher
moleeular weight portions of the extract. At times, such cool-
ing may be done deliberately to facilitate separation of thesolids from the extract and to improve the quality of the
extraet. Seleetive preeipitation of this type may be further
intensified, if desired, by addition of a preeipitating solvent,
for example a paraffinie or naphthenie hydrocarbon. The manner
in which a precipitating solvent may be advantageously used is
now well known. An example of its use is fully described in
U. 5. Patent No. 3,791,956.
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.. . .
Treatment of Low-Solids Product from Se~aration Zone
The low-solids liquid product issuing from the
separation zone 16 is conducted wit:hout intentional cooling
by a line 17 to a distillation zone 18. The primary purpose
of the distillation zone is to recover the major portion of the
solvent along with that part of the extrac-t which boils below
or in the boiling range of the solvent. Some distillate may be
]eft in the extract in order to lower the naturally high
viscosity of the extract. The temperature of the molten extract
(which, in a solvent-free state, is a solid at temperatures below
100C.) should be kept below that at which any coking of the
extract might occur.
The distillation zone may be any suitable distillation
equipment for flashing off most of the distillables, leaving a
bottoms product consisting essentially of non-distillable
extract, some solvent and whatever solids are in the feed to the
distillation zone. The vaporous products are conducted through
a conduit 19 to a fractional distillation zone 20 where they are
fractionally distilled to yield a distillate fraction suitable
for use as a distillate fuel and a higher boiling distillate
fraction which is solventO The distillate fuel fraction is with-
drawn through conduit 21 and the solvent is recycled through
conduit 12 to the liquefaction zone 10.
The coal extract is then conducted through a conduit
22 to a suitable mixing zone 23 wherein low-ash and low-sulfur
carbonaceous solids are added in sufficient quantity to form
a high solids-containing product which is pelletizable when hot,
in forming zone 25. The amount of carbonaceous solids required
for this purpose is a function of the binding properties of the
extract and of the solvent, as well as the relative proportions
of the extract and retained solvent. Furthermore, binder may
g _
: . . ' , .
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be added extraneously to supplement the extract and solvent.
If the conditions maintained in the subsequent forming zone 25
are such as to cause volatilization of the solvent, then the
pelletizable mixture may, of course, be richer in solvent. But
if the conditions ln the forming zone do no-t cause volatilization
of solvent, then the pelletizable mixture must be of the
necessary composition for pelletization. In general, the
pelletizable composition, excluding any solvent that may be
vaporized in the forming zone, is typically as follows:
Carbonaceous solids 35-75 weight percent
Extract and solvent 25-65 weight percent
where the extract is generally at least 75 weight percent of
the extract-solvent mix, and is preferably greater than
90 weight percent. The pellets will have substantially the
same composition unless the pelletization is conducted under
carbonizing conditions which result in production of some
gas and tar.
The carbonaceous solids admixed with the extract in
the mixing zone 23 are supplied through a conduit 2~. They are
preferably derived from the process itself. However, in its
broadest aspects, the process of the present invention may
resort to extraneous sources of carbonaceous solids, however
derived.
The pelletizable composition, suitably admixed in
the mixing zone, is transferred to the forming zone 25. The
primary objective of the forming zone is to form pellets out of
the pelletizable mass received from the mixing zone. The
pellets ma~ be made by any one of the many known pelletizing
processes, for e~ample, briquetting, extrusion or agglomeration,
~ 30 under carbonizing or non-carbonizing conditons a-t a temperature
above the softening point of the binder. The process selected
should be one which is adapted to be used at an elevated
.~
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~3a~
temperature at whlch the extract is fluid.
If the pellets are formed in the forming zone 25
under carbonizing conditions, that is at a temperature above
400C., the resulting pellets will be sufficiently hard to
permit handling. However, if no carbonization occurs in the
forming zone, induration of the pellets subsequent to the
forming step is required. In such event, the pellets formed
in the forming zone 25 are advanced to an induration zone 26.
Hardening of the pellets in the induration zone 26 may be
effected by heating the pellets under carbonizing conditions,
that is at a temperature above 4C0C., or by simply cooling
them below the softening point of the solution of extract and
solvent which is generally above 150C. Carbonization of the
pell~ts, whether effected in the course of pellet formation in
the forming zone or subsequently in a separate zone, yields a
vaporous product which contains a fraction corresponding to the
solvent used for the coal extraction which may be recovered for
use in the liquefaction zone 10. As will be seen later in the
description of the preferred embodimentl mixing, forming and
induration need not be performed separately, but in any suitable
or appropriate combination of steps.
JA~ Hardened pellets are withdrawn from the induration
.. ~
; zone 26 through a conduit 27. Depending upon the forming
process selected, the pellets may contain off-size pellets,
~ that is pellets which are not suitable for -the intended use,
.: either because they are too small or too large. In such event,
the off-size pellets, after suitable size adjustment, may be
recycled for use as part or all of the carbonaceous solids
. admixed with extract in the mixing zone 23. Such recycle is
shown by the lines 24 and 28. Those pellets which are within
':
the desired range may be used as is in certain operations. For
':,
,:
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~ i~3~
example, -they may serve as part of a coke oven feed, or as
solid reductant in certain ore reduction furnaces. Or they
may be subjected to a temperature between 800 and 950C. to
: yield blast furnace coke.
'
; Treatment of High Solids Prociuct from Separation Zone
~,
At least a portion of the high solids product
~- issuing from the separation zone 16 is tranferred through a
conduit 29 to a distillation zone 30 which is maintained at a
temperature sufficiently high to distill off solvent, leaving a
~ 10 hydrocarbonaceous ash-containing solid. If extract is present,
; as may well be the case unless exhaustive solvent washing has
been resorted to, the temperature maintained in the distilla-
tion zone 30 should be sufficiently high to carbonize the
` extract to coke or char and vaporous products. A suitable
. temperature is in the range of 425 to 760C. The ash-containing
,,.
solids are withdrawn from the zone 30 and conducted by a con-
duit 31 to any conventional type steam-carbon gasification
zone 32 operated under conditions to yield CH4, CO and H2. The
solid gasification residue rlch in inorganic sulfur compounds
is discharged from the system through a conduit 33. The gaseous
product is conducted by a conduit 34 to a conventional-type
gas treatment zone 35 for the recovery of hydrogen. The other
principal product CHI, is recovered through a conduit 36 as high
Btu gas. The hydrogen is conducted by a conduit 37 to the
` liquefaction zc,ne 10. As pointed out earlier, a portion of the
required coal liquefaction solvent is introduced into the
; liquefaction zone by a conduit 13. The solvenl is derived from
the distillation zone 30. The vapors issuing from the latter
zone are conducted by a conduit 3~ to a fractional distillation
zone 39 which is a conventional type. The fraction having the
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:' ' ,:
; desired boiling range for -the solvent is recovered for that
purpose, while the balance may be wi-thdrawn through conduit 40
to serve as distillate fuel. Instead of returning solvent
directly to the liquefaction zone, the solvent may first be
hydrogenated by the hydrogen from conduit 37 to thereby yield a
hydrogen-donor solvent which may then be used as the scurce of
hydrogen in the liquefaction zone, as is more fully shown in the
preferred embodiment of FIGURE 2.
PREFERRED EMBODIMENT
FIGURE 2 shows schematically a coal conversion plant
utilizing the preferred embodiment of the present invention. It
is directed specifically to the conversion of a high sulfur coal
to the low-ash and low-sulfur fuels required in a steel plant,
including fcrmcoke suitable for use in a blast furnace.
Feed Coal
;~
A high-sulfur coal is used which has a volatile
matter content of at least 20 weight percent. A typical coal
suitable for use in this preferred embodiment has the composi-
~ tion shown in Table I below:
;:
TABLE I
Proximate analysis: W-t. Percent MF* Coal
Volatile matter 41.7
Fixed carbon 45,9
Ash 11.6
Ultimate analysis: Wt. Percent MAF** Coal
~ydrogen 5-34
Carbon 78.97
- Nitrogen 1.60
; Oxygen 10.47
Sulfur 3.62
*MF means moisture-free.
**MAF means moisture-and-ash-free.
- 13 -
':
.
The feed coal is preferably ground to a finely divided state,
for example, minus 14 mesh Tyler Slandard screen, and is
freed of substa~tially all extraneous water.
(1) Coal Liquefaction Zone
The feed coal is introduced into an Extractor 50
via a conduit 510 Hydrogen donor (H-donor) solvent is intro-
duced into the Extractor via a conduit 52. The coal and the
solvent react therein to yield the desired coal extract in
;; admixture with undissolved solids.
The solvent extraction process is a non-catalytic,
continuous, countercurrent process conducted in a vertical
cylindrical vessel, at a temperature in the range of 350 to
475C., a pressure in the range of 4 to 50 kg/cm~, and a
: solvent-to-coal ratio of 1.5 to 3Ø Under such conditions,
the amount of hydrogen transferred is between 0.7 and 2.5
. (weight percent MAF coal).
The solvent is a polycyclic, aromatic hydrocarbon
~ which is liquid at the temperature and pressure of extraction,
;. and contains partially hydrogenated aromatics. It is
20 naturally derived from the hydrogenation of extract or
fractions thereof. It usually has a relatively wide distilla-
tion range with an initial atmospheric boiling point of about
.:; 200C. and a final boiling point of 500C. or even higher.
(2) Separation Zone
Following extraction, the effluent mixture of solvent,
extract and residue is conducted rapidly from the Extractor 50
so as to avoid excessive cooling of the mixture, through a
conduit 53 to a F~ydroclone system 54 consisting of one or more
hydroclones adapted to concentrate the solids preferentially
~ 14 -
.
3~
in the underflow. While the greater part of the residue is in
the product underflow from the Hydroclone system, the exact
amount is controlled, firstly to assure that both overflow and
underflow products are pumpable, and secondly to maintain the
required distribution of lo~-sulfur fuels for the steel plant.
While the organic sulfur has been reduced in the E~tractor, the
~; inorganic sulfur is still left in the solid residue. In this
preferred embodiment of the invention, the solids content of
the extract (exclufling solvent) recovered from the Hydroclone
system overflow may be in the range of 0.05 to 15 weight per-
cent, while the solids content of the total underflow from the
Hydroclone system may be in the range of 30 to 55 weight percent,
but is generally between 40 and 55 weight percent.
'
(3) Treatment of the Overflow from the Hydroclone System
The overflow from the Hydroclone system is pumped by
a pump (not shown) through a conduit 55 to a Still 56 where at
least some solvent and any light oil are fractionally distilled.
The light oil is suitably recovered (not shown) for use as
distillate fuel, while the spent solvent is witndrawn through a
conduit 57. A portion of the spent solvent is sent through a
conduit 58 to a Solvent Rehydro unit S9 while the remainder is
recycled to the Extractor 50 through a conduit 60 which connects
with conduit 52. The portion of the spent solvent which is sent
to the Solvent Renydro unit is subjected to the usual conditions
for rehydrogenation of hydrogen-donor solvents by means of
hydrogen gas introduced by conduit 61. Typical hydrogenation
conditions are as follows:
Temperature, C. - 340
Pressure - 70 Kg/cm2
H2 Rate _ 0.9 m3/Kg
Catalyst - 5/16 cm. pellets of NiS-MoS2
on Al203
LHSV - 2
- 15 -
~h~
The hydrogenation product is fractionated to recover the
rehydrogenated solvent which is returned to the Extractor
through a conduit 62 and conduit 52. The remainder is with-
drawn through a conduit 63 for use as distillate fuel.
The extract-containing portion recovered in the
Still 56 is conducted to a Pelletizer 64 through a conduit 65.
The Pelletizer consists essentially of a rotary cylindrical
kiln, usually slightly inclined from the horizontal. It
serves to mix, form and harden pellets all in the same vessel.
The extract-containing portion contains not only extract~ but
also some solvent, and in the case of this preferred embodi-
ment, less than about 5 percent by weight of solids. In order
to establish a pelletizable mass in the Pelletizer 6~, the feed
to the Pelletizer, when admixed in the Pelletizer, should have
about the following composition, excluding any solvent that may
be vaporized in the Pelletizer:
. ~
Weight Percent
Solids 60-75
Extract and Solvent25-40
The composition of the pelletizable mass is, to some extent,
dependent upon the density of the solids, the higher the density
the less binder is required. The reason fcr this is presumably
absorption of binder in the pores of the less dense solids.
As previously stated, there is generally less than
5 percent solids in the extract-containing stream to the
Pelletizer. Accordingly, it is necessary to provide a sub-
stantial amount of solids to raise the weight percent to the
required range of 60-75. This may be done in one or both of
two ways. ~'irstly, a portion of the extract feedstream is
30 diverted through a conduit 66 to an Extract LTC unit 67
adapted to subject the extract to low temperature carbonization,
- 16 -
that is to heat at 425 to 500C. whereby a char product is
obtained which is conducted to the Pelletizer through a
conduit 68. A vaporous product is also obtained, which is
conducted by a conduit 69 to a condenser 70 where the liquefiable
portion is condensed and withdrawn through a conduit 71 for use
as distillate fuel. The non-liquefiable portion is withdrawn
through a conduit 72 for use as low Btu gas.
The other way to raise the solids content of the
pelletizable mass to within the desired range is to recycle off-
size pellets from the Pelletizer through a conduit 73, a pre-
heater 74, and a conduit 75. If the solids content of the
extract feedstream is sufficiently greater than 5 percent, as
might be the case in certain non-preferred embodiments, then the
recycle pelle-ts will provide all the additional solids needed so
that carbonization of extract becomes unnecessary.
~ he pelletiz~ble mass of the desired composition is
subjected to pelletization under adiabatic low temperature carbon-
ization conditions at a temperature above 400C. as is now well
known. For example, the operation of the Pelletizer 64 is set
forth in UO S. Patent 3,401,089, granted Septemb~r 10, 1968 to
R. J. Friedrich et al. The pellets of the desired size consist
are withdrawn from a separator 76 located at the end of the
rotary kiln and conducted by a conduit 77 to a Calciner 78. The
off-size pellets, as previously stated, are recycled with
appropriate crushing as may be required to yield the desired size
consist for use in the pelletizable mass. The vaporous product
from the kiln is withdrawn through a conduit 79 to join conduit
69 leading to the condenser 70.
The Calciner 78 is adapted to heat the pellets of
.~:
-; 30 desired size, generally 60 mm x 20 mm, to a temperature between
.; 800 and 950C. at a pressure between 0 (1 atmospheric absolute)
'
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and 15 kg/cm2. The calcined pellets are withdrawn through a
conduit 80 for use as formcoke in a blast furnace.
(4) Treatment of the Underflow from the Hydroclone System
The solids-rich underflow from the Hydroclone 54 is
pumped through a conduit 81 to a Pelletizer 82 after appropriate
adjustment of the composition of the underflow to yield a
pelletizable mass in the Pelletizer. The desired composition
is generally the same as that set forth for the composition
maintained in Pelletizer 64 and is generally establlshed by
appropriate removal of solvent in the proper amount. However,
the function and operation of Pelletizer 82 are not the same as
`~ that of Pelletizer 64. In this instance, the Pelletizer 82
serves to mix and to form pellets in much the same manner as
does Pelletizer 64 but under non-carbonizing conditions, i.e.
at temperatures between 300 and 370C., high enough to vaporize
the solvent during the formation of the pe~lets. The vaporous
sc:lvent may be removed through a conduit 83 fcr condensation
and reuse. The formed pellets may need to be water-quenched
, (not shown) to harden them for subsequent handling. They are
withdrawn from the Pelletizer 82 through a conduit 84 to a
Gasifier 85.
`~ The preferred size of pelletc for use in the
Gasifier 85 is greater than 14 mesh Tyler Standard screen. If
there are any pe:Llets above about 5 cm, then it is desirable
to crush them -to less than 5 cm. The portion oE the pellets
(including the crushed oversize pellets) which is less than
14 mesh in size is separated and may be recycled to the inlet
; of the Pelletizer 82. In such case, due recognition of this
recycle stream of solids must be given in the maintenance of
the desired composition. The pellets of desired size are then
` conveyed through the conduit 84 to the Gasifier 85.
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t~,~3~
The gasifier 85 is preferably of the fixed bed ~ype,
requiring a non-caking or weakly caking carbonaceous feed for
satisfactory commercial operation. In such a gasifler, a bed
of pellets which are relatively stationary with respect to
each other moves progressively downwardly first through a
carbonization zone 86 and then through a gasification zone 87.
- Steam and oxygen are introduced into the gasification zone and
are circulated upwardly through the downwardly moving bed while
ash is suitably rejected from the bottom of the cJasifier. The
temperatures in the carbonization zone are maintained within
the range 500 to 775C. by the hot gases issuing from the gasi-
fication zone. The gasification zone is maintained at a temper-
ature in the range of 775 to 1050C. The pressure is 20 to 40
kg/cm2. The incoming pellets are carbonized in the carboniza-
tion zone, yielding tar vapors which are withdrawn with the
effluent gases via a conduit 88. The carbonized pellets move
downwardly in reactive contact with the upflowing steam and
oxygen to form CO2, CH4, H2, and C~. These pass through the
carbonization zone and into conduit 88. The effluent gas,
20 including tar and solvent vapors is passed into a condenser 89
for separate recovery of gas, solvent and tar. Solvent is
recovered from the condenser and conducted via a conduit gO to
connect with conduit 58 which ]eads to the Solvent Rehydro
unit 59. The tar-free gas is conducted by a conduit 91 to a
suitable hydrogen recovery system 92 of conventional type from
which a hydrogen-enriched gas is recovered. This gas i5 with-
drawn through conduit 61 to serve in the rehydrogenation of the
solvent. The remaining gas is wi-thdrawn through a conduit 93
to serve as a high Btu gas.
.,
.
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'',^' ' "'
The ash and sulfur contents of the spectrum of
products shown in FIGURE 2 will naturally depend upon the
specific conditions selected for each of the described essential
operations. The more severe the conditions of hydrogenation
maintained in the Extractor 50, the larger is the amount of
organic sulfur that is removed. The more effective the
separation of solids, i.e. ash, from the extract in the
Hydroclone system 54, the lower will be the ash and hence
sulfur content of the solid, liquid and gaseous products
since the major part of the inorganic sulfur will be rejected
as ash from the Gasifier 85. However, it may be desirable
from an economic point of view to accept or tolerate some
ash and sulfur, without impairing the usefulness of the
product or doing harm to the environment. The process of the
present invention permits both flexibility and selectivity
in modifying not only the distribution of products, but also
their respective compositions.
According to the provisions of the patent
statutes, the principle, preferred construction and mode
of operation of the invention have been explained and what
is considered to represent its best embodiment has been
illustrated and described. However, it should be understood
that, within the scope of the appended claims, the invention
may be practiced otherwise than as specifically illustrated
and described.
.
....
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